Several normally wheeled vehicles and particularly heavy wheeled vehicles (e.g. farming tractors, front loaders, harvesters, etc.) often have their wheels replaced by track systems which use an endless traction band or track instead of a tire for propulsion or for steering. Vehicles equipped with track systems typically have improved floatation and traction, particularly when operated over soft terrains.
Endless tracks have been used on vehicles to increase surface area in contact with the ground. This increased vehicle footprint results in a lower pressure on the ground being traversed than a conventional wheeled vehicle of the same weight.
In a typical embodiment of an endless track system, an endless track is driven by a sprocket in which teeth of the sprocket engage links of the track to drive the track and the vehicle forward. Road wheels and idler wheels are attached to the track system and roll over the track in contact with the ground. In such an embodiment, the road wheels typically do not drive the vehicle forward as only the sprocket is used for providing movement. The direct engagement of the sprocket does not allow for track slippage relative to the sprocket and/or due to friction between track and sprocket.
During operation, some components of the track systems, and more particularly the idler wheels and road wheels, can experience uneven load distribution, especially upon braking. Braking events generally prompt upward movement of the idler wheels, which affects the tension of the endless track. This is particularly true for the idler wheels located the front of the track system. As upward movement of the idler wheels is generally desired when encountering varying obstacle, terrain variation and/or debris ingestion, the tracked vehicles are typically equipped with one or more tensioner devices adapted to substantially maintain the track at a predetermined tension during operation over various terrain profiles. Such tensioner device aims at avoiding that the track slides off the sprocket and/or idlers during a sudden maneuver or a turn. Typically, the tensioner device may as well prevent excessive load from being applied to the endless track, to the sprocket wheel, and to the vehicle suspension.
Additionally, track tension may impact the power efficiency. In some situations, an over tightened or under tightened track may lead to power loss from excess friction and may accelerate the wear of the track system. However, radially upward movement of the idler wheels upon braking must be restrained as tension of the track is decreased, thus loosening the endless track leading to ratcheting of the track. As such, decreased tension in the endless track upon braking hinders the proper functioning of the track system and decreases the braking efficiency of the track system. Furthermore, upward movement of the idler wheels upon braking increases wear of the track system, in part due to ratcheting but also due to the overall deformation of the track system. As such, the tensioner in the track system aims at maintaining the perimeter defined by the wheels generally equal or superior to the nominal perimeter of the track.
Track tension is typically controlled by moving the sprocket or idler wheels that engage the track. A conventional passive mechanism for moving the sprocket or idler wheels is a track tensioner employing a grease-filled cylinder or an oil filled cylinder using an accumulator acting as a spring. Such mechanism is referred to as a dynamic tensioner. A piston in the cylinder moves as grease is added or removed through a fitting. The piston moves the sprocket or idler wheels relative to the track thereby causing the sprocket or idler wheel to either extend into the track path and increase the tension of the track or to withdraw from the path of the track and decrease the tension of the track.
Indeed, in track systems, the resultant force from the track tension and the track friction can induce a torque around the pivot supporting the idler frame which supports the idler wheels, resulting in the rotation of the idler frame thereabout. This rotation then generally causes the idler wheels located at one end of the idler frame to move circularly about the radius of the idler frame pivot point, while causing the road wheels located at the other end of the idler frame to move in the opposite direction circularly about the radius of the idler frame pivot point, resulting in an increased load on the wheels which are urged against the ground. The rotation of the idler frame can also cause the trailing portion of the track system to rise. This uneven load distribution can reduce the efficiency of the track system and even lead to premature failure thereof.
Moreover, some safety regulations in countries require that agricultural tracked vehicles be able to immobilize themselves from a given speed within a certain distance and/or meet a deceleration value. Those requirements are such that current mechanism are inefficient if not deficient at avoiding the ratcheting phenomenon as described above.
Hence, there is a need for an improved track system having a dynamic or active track tensioner which may mitigate at least some shortcomings of prior art track systems.
The required tensioner shall be able to allow rotational movement of the front wheel when the vehicle is in normal operation mode and be able to block, or limit such movement in a braking event to avoid or at least limit the ratcheting of the sprocket wheel or drive wheel.
Similar issues also exist in the design of a rear suspension for a mountain bike. In a mountain bike, the rear suspension tends to compress when the user pedals, thus the compression is reducing the efficiency of the pedaling. Solutions have been developed to adjust the damping of the suspension in relation with the shock force applied to the suspension. An example of a solution may be found U.S. Pat. No. 8,770,360 in which an inertial valve is used to modulate the damping of the suspension element. However, such solution provides a mean to maintain the suspension blocked during operation and to unlock the suspension element when an obstacle is hit. Furthermore, such solutions are configured to absorb a limited shock or force.